The hairs of aromatic goldenrod (Plate 13, Figs. 3 and 4) are larger than those of erigeron; the diameter is greater and the walls are non-porous. The apex of the hair terminates in a group of about four cells of unequal length, which are sharp-pointed. The branches of the basal cells (Plate 13, Fig. 3) are similar to the branches of the apical cells. The hairs of arnica (Plate 14, Figs. 1 and 2) have thick, strongly porous walls; the branches terminate in sharp points. The apex of the hair terminates in a single cell. The basal branches (Plate 14, Fig. 2) are much longer than special branches. [Illustration: PLATE 12 NON-GLANDULAR MULTICELLULAR HAIRS _Shepherdia canadensis_, [L.] Nutt.] [Illustration: PLATE 13 MULTICELLULAR MULTISERIATE BRANCHED HAIRS 1. Basal hairs of erigeron (_Erigeron canadensis_, L.). 2. Apical hairs of erigeron (_Erigeron canadensis_, L.). 3. Basal hairs of aromatic goldenrod (_Solidago odora_, Ait.). 4. Apical hairs of aromatic goldenrod (_Solidago odora_, Ait.).] The hair of grindelia (Plate 14, Figs. 3 and 4) has very thick walls with numerous elongated pores. The apex of the hair terminates in a cluster of cells with short, free, sharp-pointed ends. The basal branches (Plate 14, Fig. 4) are longer than the apical branches. Boneset hair (Plate 15, Figs. 1 and 2) has non-porous walls. The apex of the hair terminates in two blunt-pointed cells. The terminal wall is thicker than the side wall. Some of the branches lower down terminate in cells with very thick or solid points. The basal branches (Plate 15, Fig. 1) are longer, but the cells are narrower and more strongly tapering than are the branches of the apical part of the hair. Life-everlasting (Plate 15, Figs. 3 and 4) has uniformly thickened but non-porous walls. The hair terminates in two blunt-pointed, greatly elongated cells. The basal branches (Plate 15, Fig. 4) are narrower, slightly tapering, and the base of the branches frequently curve downward. The cell cavities of these hairs are filled with air. The walls of hairs are composed of cutin, of lignin, and of cellulose. PERIDERM The =periderm= is the outer protective covering of the stems and roots of mature shrubs and trees. The periderm replaces the epidermis. The periderm may be composed of cork cells, stone cell-cork, or a mixture of cork, parenchyma, fibres, stone cells, etc. CORK PERIDERM The typical periderm is made up of =cork cells=. Cork cells vary in appearance, according to the part of the cell viewed. [Illustration: PLATE 14 MULTICELLULAR MULTISERIATE BRANCHED HAIRS 1. Apical hairs arnica (_Arnica montana_, L.). 2. Basal hairs arnica (_Arnica montana_, L.). 3. Apical hairs grindelia (_Grindelia squarrosa_, [Pursh] Dunal). 4. Basal hairs grindelia (_Grindelia squarrosa_, [Pursh] Dunal).] [Illustration: PLATE 15